1. Field of the Invention
The present invention relates to data transfer techniques, in particular DMA techniques for use in internetworking.
2. Description of the Related Art
Direct memory access (DMA) is a well-known method of moving data between a disk or other storage system and memory by direct transfer without first copying it into processor memory.
Various types of input/output (I/O) access have been provided over computer networks for many years. These systems, which typically use technologies such as disk file or tape systems, have suffered from the overhead of the network protocol processing needed to read and copy the data from the source system, re-format the copy, and transmit the reformatted data to the receiving system. At a minimum, prior data transfers across networks have typically required copying the data in order to move it to another location after reception.
As networks move to ever-higher data rates in the megabits to gigabits per second (Mbps, Gbps) and beyond, the speed of the networks has made the centralization of storage in remote sites more feasible. However, such storage centralization and the necessary data transfer requirements have exposed the extra memory copies required by conventional network communication protocol implementations as a significant and unacceptable cost.
Networked storage data transfers are highly desired by users of storage systems. Utilizing current networking protocols in these data transfers, however, incurs high overhead costs because the endpoint in the network transfer is forced to make an extra copy of some or all of the data. As the number of blocks received per second increases, the amount of copying delay and thus overhead required to handle each block increases dramatically because each copy in a chain of copies is increased in size.
To date, the response to the problem of unacceptable overhead requirements in network remote DMA (RDMA) has been to invent entirely new protocol architectures. The logic behind these new protocol architectures, which include Fibre Channel, NGIO, Future I/O, and System I/O, and InfiniBand, has been to re-engineer the entire communications protocol to focus specifically on the RDMA task. These new architectures have also been justified by citing unspecified “performance issues” with existing protocol suites and, in particular, the TCP/IP protocol suite.
What is needed is a remote direct memory access technique that leverages from existing protocol architectures in a way that greatly reduces the amount of data copying needed to transfer large blocks of data across the network. Such an RDMA technique must also avoid (or at least minimize) modifications to the installed network hardware and software base.